Mathematical instrument



B. C. JACOB MATHEMATICAL I INSTRUMENT March 10, 1936.

3 Sheets-Sheet 1 Filed March 25, 1935 INVENTOR.

926M 1 w! W ATTORNEY.

March 10, 1936. B. c. JACOB 2,033,715

MATHEMATICAL INSTRUMENT Filed March 26, 1935 5 Sheets-Sheet 2 INVENTOR.

MM/w! ATTORNEY.

March 10, 1936. c JACOB 2,033,715

MATHEMATI CAL INSTRUMENT Fi'led March 26, 1955 3 Shees-Sheet 3 INVENTOR Hi 9 I B ATTORNEY.

s... Mar. 10, 1936 UNITED STATES PATENT [OFFICE Await: 13,125

6 Claims. (CL 33-75) v I hereinafter in connection with illustrative usesof this class.

It is therefore an object of this invention to provide an improved mathematical instrument for the solution of various mathematical problems, especially in engineering work.

Another object is to provide a mathematical instrument for applying .the principles of calculus to the solution of problems.

Another object is to provide a mathematical instrument by'which integrals and differentialsmay be derived from known functions in an improved manner.

Another object 1s to provide a mathematical instrument for determining the graphically represented integral of 'a given graphically represented function, of the graphically represented diflferential thereof.

Another object is to provide an instrument by wh ch mathematical problems may be solved and which may also be used in performing ordinary drafting operations on a drawing board.

Another object is to provide a mathematical instrument for makingmathematical computations which may be used with the so-called ,universal drafting machine.

' ing description taken in connection with theac- My invention is fully disclosed in the followcompanying' drawings, in which: v Figs. 1 and 2 are, respectively,'plan view and edge view ofone form or. embodiment ofmy in-Q" '-vention;

. 1 Fig.3 is a'view to an enlargedscale of a part ofFig.1;' q I Fig. 4 is a sectional view to an enlarged scale taken o'n'the plane l-tot Fig. 1; p f

Fig. '5'is a perspective view illustrating the em bodiment' of Fig. 1,. in'the preferred manner of use Jin connection withia drawing board, and a universal drafting machine;

Fig; 6 is a sectional view to an enlarged scale taken from the plane 6-5 of Fig. y

Fig.7 is a view illustratinggraphically, to the conventional X and Y coordinates, a function to be integrated as an illustrative use of the mathematica-l instrument of my invention;

Fig. 8is a view illustrating a step of theory underlying the practice of my invention;

Fig. 9 is a view illustrating the method of using the instrument of my invention in determining the graphically represented integral of the curve 5 of Fig. '7

Fig. 10 is a veiw illustrating a proof of the method of Fig. 9;

Fig. 11 is a view illustrating another use of the instrument in determining the said integral; 10

Figs. 12 and 13 are views similar to Fig. 1 but to, a smaller scale and illustrating. other forms in which my invention may be embodied.

In the following, the physical construction and properties of the combined drafting and mathe- 15 I matical'computing instrument embodying my invention willflrst be described, followed by a description of the method of using the instrument in making an illustrative computation. v Referring to Figs. 1 and 2 which illustrate the preferred embodiment, I have shown at I a triangular sheet or piece of transparent material such as pyroxylin plastic, celluloid or the like, such material for example as is commonly used in making drafting triangles, irregular curves, etc.

:The piece I may be of a 'size convenientto the uses'thereof which will appear hereinafter,-the piece illustrated in Fig. 1 being. approximately one-half of the preferred dimensions." Rectilinear edges 2 and 3 are provided which, in the .preferred form'illustrated, meet each other at a comer 3a at a right angle. Opposite the corner v 3a is a rectilinear edge i. The edges 2 and 3 may Other objects will beapparent to those skilled d in the-art'to which my invention appertains.

be of equal length although this is not essential.

- The edges 2, 3, and4 are made smooth for ruling lines on paper after'the manner of. ruling lines with the usual triangles.

On one face, the under face or sideof the sheet I when lying on paper on which it is to be used, v in a manner to be described, are inscribed line 4 linesi and 6 parallel respectively to the edges 2 and 3 and meeting at a common point or center I in the corner 3a of, the piece.-

Circular lines 8, 9, ill, and II, any suitable number of which-may be provided, are drawn withlthe point 1 at the center thereofand prefierably extend arcuately to the lines '5 and 8, but

I througlf the material of 50 other two holes of the erected from the line 5, 1"

ierred practice pencil point may accurately mark points on the sheet of paper IS on which the instrument rests. 1

The holes l3' are disposed in a rectilinear line according to the following grouping. Beginning at the end of the line, is a group of two holes lG-IS, then a single hole N, then a succession of groups of three holes l8 alternating with single holes l1, and a final group at the other end of two holes I6. The single holes I! are each spaced from the middle hole of the group I8, and from the outer end hole of the groups l6 by equal distances represented in Fig. 1 by the letter V, the group I8 are spaced on each side of the middle hole of the group by a. distance V/3; and the holes of the two end groups are spaced apart the distance of V/3, as shown in the drawings.

At the outer end of the line is a rectangle l9 introduced to a larger scale in Fig. 3. divided into equal parts by nine horizontal lines and ten sloping lines 2|, the rectangle preferably measuring 1"x1", and lines 22, 23, and 24 are apart, and the line 22, 1" from the rectangle IS. The cornerof the rectangle is preferably indicated by an inscribed 0 and the lines 22 to 24 by inscribed numerals 1, 2, 3, etc.

In the use of the instrument, it is laid on drawing paper on a drawing board and may be moved thereover by sliding one edge, for example the edges 2 or 3, along another straight edge such as. the edge of a triangle; but in the preof my invention, the instrument of Fig. 1 is moimted on a universal drafting machine as shown in Fig. -5; A drawing board 25, provided with suitable clip devices 26-28 for mounting a sheet of paper [5 thereon, has the primary parallel arms 21-21 of the drawing machine mounted on a base 28"secured to the board .25 by any suitableconstruction, for example by a thumb screw 29. The secondary arms 30-3001 the machine, pivoted to the elbow oted, carry on their free ends a plate 32 (see also Fig. 6). A, screw 33 .is Projected upwardly the instrument, -I, and through a plate 34 preferably riveted to the instrument I by rivets 35-35- and through the plate 32. A thumb screw or knob '36 on the screw 33 is provided to clamp the plates 32 and 34 together.

.By this means, when the knob 38 isloosened,

the instrument I may be rotated around the I screw to any desired position; then when the knob 38 is tightened, the instrument I will move bodily with the arms 30-30 of. the instrument in the well known manner to move the instrument about over the paper whereby parallel lines may be drawn by the edge 2 or the edge 3. As shown in Fig. 5 but not in'Fig. 1, the instrument may have, along the edges 2 and 3, scales 3'! and 38.

The instrument is preferably designed to measlire lengths in some unit, such as, inches or centi meters and areas in unit such as square inches or square centimeters.

above in connection scales and, the circles 8 to I I may be conveniently 3l at one endto which the free ends of the arms 21-21 are piv- 9' of unitary radius,

Y straight edge is then placed along v when the unit is to be ,an' inch, and-when the lines 0, 1, 2, and 3, described withFigs. 1 and 3, arel"; apart, the scales 3! and 38 may be suitably inch sented integral-of a graphically represented function will now be described as an illustrative use thereof.

The'curve 39 of Fig. 7 represents, graphically, some function of rand 1/, which function may in fact be impossible of algebraic expression, and unknown, except graphically. Suppose it be desired to ascertain the area represented by the curve 39, namely the area between the curve and 1 the base coordinate X. We will first assume that the curve 40 of Fig. 8 is the integral of the curve 39. Then for any value of x, the ordinate u, having the value of yda: integratedfrom zero to :r, is a measure of the shaded area under the curve 39 from zero 15 to :c.

A tangent ab may now be drawn to the curve 40 at the point a at the top of the ordinate u, and

the slope thereof will be du/da'. If a unitary base such as 1" be substituted for dz, then the slope 20 of the tangent ab will be yZ/l, or, yl. That is to say, yl=du/da:. In the equation yl=du/d:r, we can substitute for du the quantity y.da:, hence y and yl are equal. Thus, we find that the slope of the integral curve 40 at any point a may be 25 represented by y/Z or y where l is the unitary I length chosen as above described. The integral curve 40 was arbitrarily chosen for purposes of analysis, but the actual integral curve may now be found by finding a succession of points a at 3;) successive values of 1:, defining a curve, the slope of which at each pointa, or at each value of 2:, may be represented by y, 3 being taken from curve 39 for the corresponding value of :c.

To use the above described instrument to find such an integral curve,.the following process is folliwed, with reference to Fig. 9. The given curve 39 is reproduced from Fig. 7. vA number of primary ordinates 4I-42, 43-44, 45-46, and 41-48, are drawn to the base X, the ordinates 40 "-42 and 41-48 being end ordinates. Secondary ordinates 49-50, 5l-52, and 53-54 are drawn between successive pairs of the primary ordinates. The ordinate 49-50 is so chosen that when horizontal lines 42-55 and 50-44 are 45 drawn. the shaded area 56 below the curve will be equal to the shaded area 51 above the curve.- The areas 56 and 51 may be made equal by inspection and this is facilitated if the curve is In a similar way. 50 I on the drawing, Fig. 9, with the center ion the X axis extended to the left, and with the circle tangent to the ordinate "-42 at the X axis. The instrument is then rotated around the center I, keeping the circle ea) tangent as described, until the line 6 intersects the top 42 of the first ordinate. An angle of slope for the line 6 is thus determined. A the-edge 2 of the instrument I, to guideit (or in" the preferred form illustrated in Fig. 5, the knob 35 is tumed' -to fix the instrument in the determined position) and the edge 3 of the-instrument is then moved, parallel to itself, until it intersects the point 4| and the line 41-65 is drawn atthe predeter the ordinate The instrument is thenagain set up with the center l on the line X and with the-curve 8 tangent to the ordinate 43-44, and is rocked unmined slope from the point 4| to 48-50.

' spasms edge, from the point 65 to ordinate B l-6 2 extended, at 62. x

The instrument is again set up with the circle 9 tangent to the ordinate 46-46, and the instrument is rocked until the line 6 intersects the point 46, and then the edge 3 is moved bodily until it intersects the point 62 anda line is drawn from the point 62'to the ordinate 53-54 extended, as at 63.

The instrument is finally set up with the circle 9 tangent to the ordinate 41-46 and rocked um i til the line 6 intersects the point 49 and then the edge 3 is moved to draw a line from the point 63 to the ordinate 41-48 extended, as at 64.

The' broken line curve 66 which now may be drawn tangent to the line 4i-65-62-63-64 at points 4i, 61, 68, and 69, is the desired integral curve. That the curve 66 is the desired integral curve, 1. e. has ordinates that are measures of the area under the given curve 39 at all values of area under the curve 39 plus the shaded area61.

Therefore, the sum of these two rectangles equals the area under the curve 99 and therefore the height 49-65 plus the height 69-61 or 43-61 XR equals the area under the curve 99 from 4| to 49, B; being unity or in this case 1. Thus, the J 'height 43-61 a measure of the area under the curve 99 from-to 43.

I the ordinates to the curve 39 are drawn closer together. the approximate segmental integral curve- In a similar manner, the ordinate 45-66 is found to be a measure of the area under'the curve 99 from 4i to 45; and the ordinate 41-64-is found to be 4i to 41.

In carrying out the above described method, if

will closely approximate a continuous curve closely enough so that the curve 66 will not have to be drawn. Furthermore, if the curve to be integrated is drawn on cross-section paper,-itwill not be necessary-to estimate the position of the secondary ordinates by estimating equal areas above and below the curve', butinstead these sec-- ondary ordinates may be taken as averageordinates betweenv the primary ordinates to give the desired degree ofaccuracy.

As an alternative method step, instead of selecting ordinates as above described to give areas such as 66 and 61 below and above the curve 39, ordinates may be determined from Simpson's ding-2714+ hn), where n is an even number ofequal spaces having the width V, with end ordinates ho and hn. To apply this principle, the instrument I .(see Fig. 11 wherein a part of the instrument I is illustrated'to enlarged scale) is rotated around with respect to the given curve :39 so that the outer hole of the group I6, namely the hole", coincides at its center with the end ordinate. 4l-42 of the curve, -extended ,downwardly; and so that the center hole of one of a measure of the entire area from the groups 16, such for example as the hole 1|, coincides with the other end ordinate, 41-46 of the curve, extended. With the instrument in this position, the pencil as shown in Fig. imay be inserted into all of holes between the holes 16 and 1|, making poin n the paper and then the instrument may be moved and parallel ordinates drawn through these points Points are thereby determined on the curve 99 by lines drawn through the holes I1 '01 the one-hole groups, for example the point 14; and horizontal v lines drawn through the curve at these points of intersection therewith will determine a plurality of rectangles as shown in Fig. 10 which may then be drawn. These rectangles while clarifying this explanation, need not be actually drawn in prac1 6108., a J

It will be observed that the width of these rectangles will, in succession, have the relation V/3, 4V/3, 2V/3, 4V/3 V/3,-which is the relationship called for by Simpson's rule, this resulting from the above-described spacing of the holesin the instrument, the horizontal distance'from each single hole'l1qto the middle hole of the group i6 being of the value V. all as shown in Fig. 11.

By the method described in detail in connec-- tion with Fig. 9, using aunitary radius R=l, a slope is now found to the top or the first ordinate 4i-42 and the first section of the integral curve ii-12 is drawn. A slope is then found to the top of the ordinate 13-14 and with this slope the next section of the integral line is drawn from 12 to 15. A slope is then found to the top of the ordinate 16-11 to which slope the next section of the integral line is drawn, from 15 to". This process is continued to complete the integral line indicated generally at 19. For convenience in accurately measuringthe lengths of lines, or' distances along a li'nebetween chosen points, I have provided the rectangle i9'and associated lines above referred to;-

" 6 and with the end of the line 96' on the line 23 until the other end of the line coincides with one of the diagonals Ii. The fractional length of the line is read in decimals, as follows:

Counting from the zero point, the end of the line lies on the fourth diagonal of the group 2|,

so that the first number to the right of the decimal point will be 4; and the end of the line also lies on the sixth parallel or horizontal line of the group 26 and therefore the second decimal figure is s and the length of the line so therefore is 2.46". e

In the foregoing Ihave described one illustrative use of the instrument, namely in determining integrals. It will be-obvious that diflerentials may be obtained in the reverse order,

using circle 9a, whose center is on the corner 90,

to mark along edge 2 'or 3. A very great variety 'of diflerent kinds of problems. arithmetical, algebraic, geometrical and involving calculus, may

be solved; but it is deemed unnecessary to expand this application to describe all of them.

' While as' stated above the instrument may be moved along ,an edge to position the inscribed lines thereon, such as the edge of a triangle or straight edge, the preferred form is that illustrated in Fig. 5 where the instrument is made as an integral part of a drafting machine of the .universal or double-parallelogram-movement type. Other-forms are-shown in Flgs. 12 and 13 wherein the sheet of transparent material H or 82 has secured thereto an attaching device 83 of well known form by which the instrument may beattached to the conventional form and construction of "universal drafting machine.

While the lines 5 and 8 meeting at the. point I are drawn at a right angle to each other in.

the form of Fig. 1 above described. this is,not essential. These lines may be at an acute angle to each other as shown at in and 6a in Fig. 13, or at at obtuse angle to each other as shown at la,

-' la, or ta, 8a in Fig. 13. And the edges s4 and I! and and ll, being parallel to the lines 5a, to and la, la, may be used inconnection with these lines as'the edges 2 and I are used in connection with the lines 5 and 6 of the described form.

In the form of Fig; 12, a line it may be used with either of two lines, lb, and parallel edges 1 88' and 89 are'provided to transfer the slope of to one-thirdof the-said single perforation tomid -to work with curves or other the line 5b.

Thus "my invention may be embodied in an almost infinite number of shapes which need not be illustrated here.

Preferably, the engraved lines are, as above referred to, on the under side of the instrument and may be colored'black, red or other contrasting color-to render their use more accurate. Several circles, such as s to II, in the form of Fig. 1,

and corresponding circles in the other illustrated forms, are provided; either of which may be taken as having the radius of unitary length above described, and are convenient where it is desired quantities of dif-' ferent dimensional scale. r

As will now be.apparent, my invention is not :limited to the exact details of construction shown .and described and many modifications other than those illustrated and described may be made within the spiritxof my invention without sacriflcing'its advantages and within the scope of the appended claims. I claim: l. A mathematical instrument comprising a sheet-like element of transparent material having a rectilinear line ruling edge, an inscribed rectilinear line parallel to the ruling edge, a circular arc having its center in said inscribed rectilinear line. and a row of pen ilelioin 0611 1 1118 p rforations in rectilinearly groups, alternate groups comprising a single perforation and three perforations respectively, the singleperforations being tion groups being spaced from the middle perforatlons on each side thereof by an amoimt equal die perforation spacing. v

2. A mathematical instrument comprising a sheet-like element, supporting means. connected to the element comprising a plvotupoh which the element may beand means i to lock the element against rotation in any rotated position, and means to support'the supporting means and permitting universal parallel bodily movement of the supporting means and locked ele ment,-and the sheet-like element having farow of pencil-point centering perforations extending therethrough in rectilinearlyspaced groups,.al-

l ternate groups comprising asingle perforation and; three perforations respectively, thesingle equallyspacedfromthemiddleper "forations of,.the three perforation groups, and

the other two perforations of the three perforaperforations beingequally spaced from the middl perforations of the three perforation groups, and the other two perforations of the three perforation groups being spaced from the middle perforations-on each side thereof by an amount equal to one-third of the said single perforation to middle perforation spacing.

. s. A mathematicalinstrument for determining a graphic diflerential function from an integral fimction graphically represented by a curve drawn to a base line and with a plurality of ordinates.

intersecting the curve, the instrument compris-v ing a sheet of transparent material having a rec tilinearruling edge, a circular arc an arc center and a rectilinear line engraved on the sheet, the line being in a direction radial to the arc and parallel to the ruling edge and having a portion extending outwardly beyond the are for a distance equal to at lehst the arc radius, the instrument adapted tobe' laid over the integral curve in successive positions with the arc center on the base line and the arc tangent tolsuccessive ordi-- function graphically represented by a' curve drawn to a base line with a plurality of ordinates intersecting the cm. the instrument comprising a sheet of transparent material having a rec tilinear ruling edge, a circular are, an arc center and a rectilinear line engraved on the sheet. thelinebein'gin a direction radial 'tothearcand parallel to the ruling edge and having a portion extending outwardly beyond the are for a dis-.

thnce strument adapted to be laid over the integral curve in successive positions with the arc center equaltoatleast'the arcradius; them-- on the base line and the arc tangent to successive ordinates whereby in each position the instrument may" be rotated about the center tov cause the rectilinear line to coincide with the point of intersection of the ordinates with the integral curve, to determine a succession of slopes for the ruling edge, .and a second edge on the sheet for en.-

t with a straight edged guide along which the element may be bodily moved to move the ruling. edge to successive parallel positions.

5'. A mathematical instrument for determining a graphic differential function-from an integral "function graphically represented by acurve drawn to a base line and with aplurality of ordinates intersecting the curve, the instrument comprising abheet of transparent material having a rectilinear ruling edge,- a'clrcular are, an arc center and a rectilinearline'engraved on the sheet, the

linebeinginadirectionradial tothe arc and parallel to the ruling ed e and having a portion extending outwardlybeyond the are for a dis- 'tance equal to alt-least the arc radius, the instru ment adapted to belaid over the integral curve in successive positions with the arc center on the base line and thearc tangent to successive ordinates whereby in each position the instrument may be rotated about'the center to cause the rectilinear line to coincide with the point or intersection-of the ordinates with the integral curve. to determine a successionof slopes for therul and a edge on the sheetforengageliient with a straight edged guide along which the element maybe bodily'moved to move the ruling edge to successive parallel positions, and supporting means connected to the sheet comprising a pivot upon which the sheet. may be rotated and comprising means to lock the sheet against rotation in any rotated position and means to support the supporting means and permitting universal parallel bodily movement of the supporting means and locked element.

6. A mathematical instrument comprising a sheet like element, and a row of pencil-point centering perforations in'rectilinearly spaced groups,

alternate groups comprising a single perforation and three perforations respectively, the single perforations being equally spaced from the middle perforations of the three perforation groups, and the other two perforations of the three perforation groups being spaced from the middle perforations on each-side thereof by an amountequal to one-third of the said single perforation to middle perforation spacing.

BRENT C. JACOB. 

